* selfdrive: add sys module to exit call
exit() is a helper for interactive shell. Let's explicit
use the module sys.
* selfdrive: tomstoned.py use constant for /data/tombstones/
Instead of use multiple times a string for
the data dir, use a variable.
old-commit-hash: 5a9d89ed42ddcd209d001a10d7eb828ef0e6d9de
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